1. Field of the Invention
The present invention generally relates to fabrication of a functional device mounting board, using an ejector to form a functional device on a substrate. More particularly, the present invention relates to an apparatus and a system for fabricating the functional device mounting board, as well as a functional device mounting board itself fabricated using the apparatus or the system.
2. Description of the Related Art
In recent years, luminescent devices (or light-emitting devices) using organic materials have been developed for use in a spontaneous luminescent display, which has been spreading in place of a liquid crystal display. In general, the luminescent device is formed using a photolithography technique to pattern a layer of a functional material into a predetermined shape. For example, it is-known that an organic electroluminescent (hereinafter, referred to as “organic EL”) device is fabricated by forming a layer of a low molecular-weight material by vapor deposition (or vacuum evaporation), and then patterning the layer by photolithography. See “Organic Electroluminescent Diodes”, C. W. Tang and S. A. VanSlyke, Appl. Phys. Lett. 51, 913 (1987). To fabricate a color organic EL device, different luminescent materials are formed on prescribed pixels by vapor deposition. However, since vacuum evaporation and photolithography are high-cost processes requiring a number of steps, it is disadvantageous to employ these techniques to fabricate luminescent devices over a wide area.
To overcome this problem, the applicant has come across an idea that inkjet droplet ejection means can be used to place a functional material at a desired position, without employing high-cost processes, such as vacuum evaporation and photolithography. Inkjet droplet ejection means are disclosed in U.S. Pat. Nos. 3,060,429, 3,298,030, 3,596,275, 3,416,153, 3,747,120, and 5,729,257. It is expected that a technique of inkjet droplet ejection can be replaced for photolithography, and that the inkjet technique can realize more stable formation of a functional device at low cost and a high yield rate.
For example, when fabricating an organic EL device as an example of the functional device, a pattern of a hole-transporting layer and a light-emissive layer can be formed on a transparent electrode substrate by ejecting a solution, in which a hole-transporting material and a luminescent material are dissolve or dispersed in a solvent, from the inkjet head.
The same idea is disclosed in JPA2000-323276 and JAP2001-60493. However, these publications only discuss the materials for organic EL devices suitable to the inkjet method, and do not sufficiently refer to either an apparatus for forming such a functional device on a substrate using an inkjet technique, or a functional device mounting board fabricated using the inkjet technique.
Applying the inkjet technique to fabrication of functional devices is not easy because the conventional inkjet technique is limited to ejecting ink onto paper. There are still many unsolved factors concerning how to eject a solution containing a functional material onto a substrate in a stable manner. Especially, a great deal of work is required to realize a group of functional devices formed on a substrate at highly precise patterns efficiently.